如何改进此exception重试方案？

我有一个我正在调用的Web服务方法，它是第三方和我的域之外。 出于某种原因，Web服务偶尔会出现网关超时。 它的间歇性和在尝试失败后直接调用它可以成功。

现在我有一个编码困境，我有代码应该做的伎俩，但代码看起来像业余时间，你会在下面看到。

这是非常糟糕的代码，还是可以接受的？ 如果不能接受，我该如何改进呢？

在看的同时请努力保持笔直。

try { MDO = OperationsWebService.MessageDownload(MI); } catch { try { MDO = OperationsWebService.MessageDownload(MI); } catch { try { MDO = OperationsWebService.MessageDownload(MI); } catch { try { MDO = OperationsWebService.MessageDownload(MI); } catch { try { MDO = OperationsWebService.MessageDownload(MI); } catch (Exception ex) { // 5 retries, ok now log and deal with the error. } } } } } 

Answer 1

你可以循环完成。

 Exception firstEx = null; for(int i=0; i<5; i++) { try { MDO = OperationsWebService.MessageDownload(MI); firstEx = null; break; } catch(Exception ex) { if (firstEx == null) { firstEx = ex; } Thread.Sleep(100 * (i + 1)); } } if (firstEx != null) { throw new Exception("WebService call failed after 5 retries.", firstEx); } 

Answer 2

这是您尝试的另一种方式：

 // Easier to change if you decide that 5 retries isn't right for you Exception exceptionKeeper = null; for (int i = 0; i < MAX_RETRIES; ++i) { try { MDO = OperationsWebService.MessageDownload(MI); break; // correct point from Joe - thanks. } catch (Exception ex) { exceptionKeeper = ex; // 5 retries, ok now log and deal with the error. } } 

我认为它更好地记录了意图。 代码也少了; 更容易维护。

Answer 3

到目前为止，所有答案都假设对任何exception的反应都应该是重试操作。 这是一个很好的假设，直到它是一个错误的假设。 您可以轻松地重试损坏系统的操作，因为您没有检查exception类型。

你几乎不应该使用一个简单的“ catch ”，也不应该使用“ catch (Exception ex) 。”捕获一个更具体的例外 – 你知道可以安全恢复的例外。

Answer 4

尝试一个循环，有一些限制：

 int retryCount = 5; var done = false; Exception error = null; while (!done && retryCount > 0) { try { MDO = OperationsWebService.MessageDownload(MI); done = true; } catch (Exception ex) { error = ex; } if (done) break; retryCount--; } 

Answer 5

您应该使用递归（或循环），并且只应在您遇到预期错误时重试。

例如：

 static void TryExecute(Action method, Func retryFilter, int maxRetries) where TException : Exception { try { method(); } catch(TException ex) { if (maxRetries > 0 && retryFilter(ex)) TryExecute(method, retryFilter, maxRetries - 1); else throw; } } 

编辑 ：循环：

 static void TryExecute(Action method, Func retryFilter, int maxRetries) where TException : Exception { while (true) { try { method(); return; } catch(TException ex) { if (maxRetries > 0 && retryFilter(ex)) maxRetries--; else throw; } } } 

---

您可以尝试通过Thread.Sleep来防止retryFilter未来错误。

如果上次重试失败，则会抛出最后一个exception。

Answer 6

这是我们正在使用的一些重试逻辑。 我们不会这么做很多，我会把它拉出来并将其记录为我们的重试模式/标准。 我第一次写这篇文章的时候不得不放弃它，所以我来到这里看看我是否正确地做到了。 看起来像我。 以下版本已完全注释。 有关未注释的版本，请参见下文。

 #region Retry logic for SomeWebService.MyMethod // The following code wraps SomeWebService.MyMethod in retry logic // in an attempt to account for network failures, timeouts, etc. // Declare the return object for SomeWebService.MyMethod outside of // the following for{} and try{} code so that we have it afterwards. MyMethodResult result = null; // This logic will attempt to retry the call to SomeWebService.MyMethod for (int retryAttempt = 1; retryAttempt <= Config.MaxRetryAttempts; retryAttempt++) { try { result = SomeWebService.MyMethod(myId); // If we didn't get an exception, then that (most likely) means that the // call was successful so we can break out of the retry logic. break; } catch (Exception ex) { // Ideally we want to only catch and act on specific // exceptions related to the failure. However, in our // testing, we found that the exception could be any type // (service unavailable, timeout, database failure, etc.) // and attempting to trap every exception that was retryable // was burdensome. It was easier to just retry everything // regardless of the cause of the exception. YMMV. Do what is // appropriate for your scenario. // Need to check to see if there will be another retry attempt allowed. if (retryAttempt < Config.MaxRetryAttempts) { // Log that we are re-trying Logger.LogEvent(string.Format("Retry attempt #{0} for SomeWebService.MyMethod({1})", retryAttempt, myId); // Put the thread to sleep. Rather than using a straight time value for each // iteration, we are going to multiply the sleep time by how many times we // have currently tried to call the method. This will allow for an easy way to // cover a broader range of time without having to use higher retry counts or timeouts. // For example, if MaxRetryAttempts = 10 and RetrySleepSeconds = 60, the coverage will // be as follows: // - Retry #1 - Sleep for 1 minute // - Retry #2 - Sleep for 2 minutes (covering three minutes total) // - Retry #10 - Sleep for 10 minutes (and will have covered almost an hour of downtime) Thread.Sleep(retryAttempt * Config.RetrySleepSeconds * 1000); } else { // If we made it here, we have tried to call the method several // times without any luck. Time to give up and move on. // Moving on could either mean: // A) Logging the exception and moving on to the next item. Logger.LogError(string.Format("Max Retry Attempts Exceeded for SomeWebService.MyMethod({0})", MyId), ex); // B) Throwing the exception for the program to deal with. throw new Exception(string.Format("Max Retry Attempts Exceeded for SomeWebService.MyMethod({0})", myId), ex); // Or both. Your code, your call. } } } #endregion 

我喜欢Samuel Neff使用exception变量来查看它是否完全失败的例子。 这会使我的逻辑中的一些评估变得更简单一些。 我可以去任何一个方向。 不确定这两种方式是否具有明显优势。 但是，在这个时间点，我不会改变我们的做法。 重要的是要记录你正在做的事情，以及为什么有些白痴不会在你身后出现并捣乱一切。

但是，为了获得更好的想法，如果代码是更短或更清洁的方式或其他方式，我提出了所有的评论。 它们出现的线数完全相同。 我继续编译了两个版本并通过Reflector Code Metrics运行它们并获得以下内容：

 Metric: Inside-Catch / Outside-For CodeSize: 197 / 185 CyclomaticComplexity: 3 / 3 Instructions: 79 / 80 Locals: 6 / 7 

catch中的最终exception逻辑（22行）：

 MyMethodResult result = null; for (int retryAttempt = 1; retryAttempt <= Config.MaxRetryAttempts; retryAttempt++) { try { result = SomeWebService.MyMethod(myId); break; } catch (Exception ex) { if (retryAttempt < Config.MaxRetryAttempts) { Logger.LogEvent(string.Format("Retry attempt #{0} for SomeWebService.MyMethod({1})", retryAttempt, myId); Thread.Sleep(retryAttempt * Config.RetrySleepSeconds * 1000); } else { Logger.LogError(string.Format("Max Retry Attempts Exceeded for SomeWebService.MyMethod({0})", MyId), ex); throw new Exception(string.Format("Max Retry Attempts Exceeded for SomeWebService.MyMethod({0})", myId), ex); } } } 

for-loop之后的最终exception逻辑（22行）：

 MyMethodResult result = null; Exception retryException = null; for (int retryAttempt = 1; retryAttempt <= Config.MaxRetryAttempts; retryAttempt++) { try { result = SomeWebService.MyMethod(myId); retryException = null; break; } catch (Exception ex) { retryException = ex; Logger.LogEvent(string.Format("Retry attempt #{0} for SomeWebService.MyMethod({1})", retryAttempt, myId); Thread.Sleep(retryAttempt * Config.RetrySleepSeconds * 1000); } } if (retryException != null) { Logger.LogError(string.Format("Max Retry Attempts Exceeded for SomeWebService.MyMethod({0})", MyId), ex); throw new Exception(string.Format("Max Retry Attempts Exceeded for SomeWebService.MyMethod({0})", myId), ex); } 

Answer 7

我正在使用以下通用方法进行重试方案。 我特别想提请注意PreserveStackTrace方法，它有助于保留完整的调用堆栈跟踪，因为（因为我学到了很难的方法）， throw或throw ex都不会产生完整的调用堆栈跟踪信息。

 public static void RetryBeforeThrow(Action action, int retries, int timeout) where T : Exception { int tries = 1; do { try { action(); return; } catch (T ex) { if (retries <= 0) { PreserveStackTrace(ex); throw; } Thread.Sleep(timeout); } } while (tries++ < retries); } /// 
 /// Sets a flag on an  so that all the stack trace information is preserved /// when the exception is re-thrown. /// 
 /// This is useful because "throw" removes information, such as the original stack frame. ///  public static void PreserveStackTrace(Exception ex) { MethodInfo preserveStackTrace = typeof(Exception).GetMethod("InternalPreserveStackTrace", BindingFlags.Instance | BindingFlags.NonPublic); preserveStackTrace.Invoke(ex, null); } 

Answer 8

正如其他人都指出的那样，正确的方法是使用某种MAX_RETRY将try / catch包装在某个循环中。

您还可以考虑在每次循环迭代之间添加超时。 否则，在瞬态问题有机会自行解决之前，您可能会烧掉重试计数器。

Answer 9

看来你有你需要的答案，但我想我会发布这个链接， 什么是行动政策？ ，我发现提供了一个更优雅的解决方案。 Lokad有一些相当迷宫的实现，但是这个人的逻辑非常可靠，而你最终编写的最终代码非常简单。

Answer 10

 int cnt=0; bool cont = true; while (cont) { try { MDO = OperationsWebService.MessageDownload(MI); cont = false; } catch (Exception ex) { ++cnt; if (cnt == 5) { // 5 retries, ok now log and deal with the error. cont = false; } } } 

更新：基于评论的固定代码。